CN105981455B - Method and apparatus for indicating a change of coverage enhancement mode in a wireless communication system - Google Patents

Abstract

A method and apparatus for indicating a change of a Coverage Enhancement (CE) mode in a wireless communication system are provided. CE modes for coverage enhancement may be defined. A User Equipment (UE) determines whether a CE mode is changed. If it is determined that the CE mode is changed, the UE is detached from the network and re-attached to the network based on the changed CE mode.

Description

Method and apparatus for indicating a change of coverage enhancement mode in a wireless communication system

Technical Field

The present invention relates to wireless communication, and more particularly, to a method and apparatus for indicating a change of a Coverage Enhancement (CE) mode in a wireless communication system.

Background

Universal Mobile Telecommunications System (UMTS) is a third generation (3G) asynchronous mobile communication system that operates in Wideband Code Division Multiple Access (WCDMA) based on european systems, global system for mobile communications (GSM), and General Packet Radio Service (GPRS). The Long Term Evolution (LTE) of UMTS is under discussion by the third generation partnership project (3GPP) to standardize UMTS.

3GPP LTE is a technology for enabling high-speed packet communication. Many schemes have been proposed for LTE goals including the intent to reduce user and provider costs, improve quality of service, and expand and improve coverage and system performance. The 3gpp lte requires, as high-level requirements, reduction in cost per bit, increase in service availability, flexible use of a frequency band, simple structure, open interface, and appropriate power consumption of a terminal.

Machine Type Communication (MTC) is an important revenue stream for operators and has great potential from the operator's perspective. There are several industry forums that address efficient machine-to-machine (M2M) systems by developing some industry members of new access technologies dedicated to MTC. It is then more efficient for the operator to be able to serve MTC User Equipment (UE) using the already deployed radio access technology. It is therefore important for operators to understand whether LTE should be a competitive radio access technology that is effectively supported for MTC. It is envisaged that a large number of MTC UEs will be deployed, large enough to create their own economic system. Reducing the cost of MTCUs is an important driving element in implementing the concept of the "Internet of things". Mtues for many applications will require low operating power consumption and desire to communicate with very small numbers of burst transmissions.

In addition, there is a substantial market for use cases where devices will be deployed deep inside buildings requiring coverage enhancement, compared to the defined LTE cell coverage footprint. Various approaches have been discussed for coverage enhancement for MTC UEs.

Some MTC UEs may be installed in basements of residential buildings or in locations shielded by insulation foiled on the underside, in metallized windows, or in traditional thick-walled building construction. These MTC UEs may experience significantly large penetration loss to the radio interface compared to ordinary LTE UEs. Therefore, coverage enhancement may be required for these MTC UEs. MTC UEs in extreme coverage scenarios may have characteristics such as very low data rates, large delay tolerance, and no mobility, and therefore, some messages/channels may not be required.

Depending on the situation, the coverage enhancement may be changed. In such a case, a mode for indicating a change of the coverage enhancement mode may be required.

Disclosure of Invention

Technical problem

A method and apparatus for indicating a change of a Coverage Enhancement (CE) mode in a wireless communication system are provided. The present invention provides a method for performing User Equipment (UE) initiated detach and re-attach if the CE mode changes.

Technical solution

In one aspect, a method for indicating a change in a Coverage Enhancement (CE) mode by a User Equipment (UE) in a wireless communication system is provided. The method comprises the following steps: determining, by the UE, whether the CE mode is changed; if the CE mode is determined to be changed, the UE is separated from the network; and re-attaching the UE with the network based on the changed CE mode.

In another aspect, a User Equipment (UE) configured to indicate a change in Coverage Enhancement (CE) mode in a wireless communication system is provided. The UE includes a Radio Frequency (RF) unit configured to transmit or receive a radio signal; and a processor coupled to the RF unit and configured to determine whether the CE mode is changed; if it is determined that the CE mode is changed, the CE mode is detached from the network and reattached to the network based on the changed CE mode.

Advantageous effects

Unnecessary repetition of messages for coverage enhancement can be avoided.

Drawings

Fig. 1 shows an LTE system architecture.

Fig. 2 shows a block diagram of the architecture of a typical E-UTRAN and a typical EPC.

Fig. 3 shows a block diagram of a user plane protocol stack of an LTE system.

Fig. 4 shows a block diagram of the control plane protocol stack of the LTE system.

Fig. 5 shows an example of a physical channel structure.

Fig. 6 illustrates an example of a method for indicating a change of a CE mode according to an embodiment of the present invention.

Fig. 7 illustrates another example of a method for indicating a change of a CE mode according to an embodiment of the present invention.

Fig. 8 illustrates a wireless communication system implementing an embodiment of the present invention.

Detailed Description

The techniques described below can be used in various wireless communication systems such as Code Division Multiple Access (CDMA), Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Orthogonal Frequency Division Multiple Access (OFDMA), single carrier frequency division multiple access (SC-FDMA), and so on. CDMA can be implemented in a radio technology such as Universal Terrestrial Radio Access (UTRA) or CDMA-2000. TDMA can be implemented in a radio technology such as global system for mobile communications (GSM)/General Packet Radio Service (GPRS)/enhanced data rates for GSM evolution (EDGE). OFDMA can be implemented in radio technologies such as Institute of Electrical and Electronics Engineers (IEEE)802.11(Wi-Fi), IEEE802.16 (WiMAX), IEEE 802-20, evolved UTRA (E-UTRA), and the like. IEEE802.16m is an evolution of IEEE802.16 e and provides backward compatibility with IEEE802.16 based systems. UTRA is part of the Universal Mobile Telecommunications System (UMTS). Third generation partnership project (3GPP) Long Term Evolution (LTE) is part of evolved UMTS (E-UMTS) using E-UTRA. 3GPP LTE uses OFDMA in the downlink and SC-FDMA in the uplink. LTE-advanced (LTE-a) is an evolution of 3GPP LTE.

For clarity, the following description will focus on LTE-a. However, the technical features of the present invention are not limited thereto.

Fig. 1 shows an LTE system architecture. Communication networks are widely deployed to provide various communication services such as voice over internet protocol (VoIP) through IMS and packet data.

Referring to FIG. 1, an LTE system architecture includes one or more user equipments (UEs; 10), an evolved UMTS terrestrial radio access network (E-UTRA), and an Evolved Packet Core (EPC). The UE 10 refers to a communication device carried by a user. The UE 10 may be fixed or mobile and may be referred to by other terms such as Mobile Station (MS), User Terminal (UT), Subscriber Station (SS), wireless device, etc.

The E-UTRAN includes one or more evolved node bs (enbs) 20, and a plurality of UEs may be located in one cell. The eNB 20 provides the UE 10 with endpoints of the control plane and the user plane. The eNB 20 is generally a fixed station that communicates with the UE 10 and may be referred to as another term, such as a Base Station (BS), an access point, etc. One eNB 20 may be deployed per cell.

Hereinafter, Downlink (DL) denotes communication from the eNB 20 to the UE 10, and Uplink (UL) denotes communication from the UE 10 to the eNB 20. In the DL, the transmitter may be part of the eNB 20 and the receiver may be part of the UE 10. In the UL, the transmitter may be part of the UE 10 and the receiver may be part of the eNB 20.

The EPC includes a Mobility Management Entity (MME) and a System Architecture Evolution (SAE) gateway (S-GW). The MME/S-GW 30 may be located at the end of the network and connected to an external network. For clarity, the MME/S-GW 30 will be referred to herein simply as a "gateway," but it should be understood that this entity includes both an MME and an S-GW.

The MME provides the eNB 20 with information including non-access stratum (NAS) signaling, NAS signaling security, Access Stratum (AS) security control, inter-Core Network (CN) node signaling for mobility between 3GPP access networks, idle mode UE reachability (including execution and control of paging retransmissions), tracking area list management (for UEs in idle and active modes), Packet Data Network (PDN) gateway (P-GW) and S-GW selection, MME selection for handover in case of MME change, Serving GPRS Support Node (SGSN) selection for handover to 2G or 3G 3GPP access networks, roaming, authentication, bearer management functions including dedicated bearer establishment, various functions supporting Public Warning System (PWS) including Earthquake and Tsunami Warning System (ETWS) and Commercial Mobile Alarm System (CMAS) message transmission. The S-GW host provides various functions including per-user based packet filtering (through, for example, deep packet inspection), lawful interception, UE Internet Protocol (IP) address assignment, transport level packet tagging in DL, UL and DL service level billing, gating and rate enhancement, DL rate enhancement based on access point name aggregation maximum bit rate (APN-AMBR).

An interface for transmitting user traffic or control traffic may be used. The UE 10 is connected to the eNB 20 via a Uu interface. The enbs 20 are connected to each other via an X2 interface. The neighboring eNB may have a mesh network structure with an X2 interface. A plurality of nodes may be connected between the eNB 20 and the gateway 30 via the S1 interface.

Fig. 2 shows a block diagram of the architecture of a typical E-UTRAN and a typical EPC. Referring to fig. 2, the eNB 20 may perform functions of selection of the gateway 30, routing toward the gateway 30 during Radio Resource Control (RRC) activation, scheduling and transmission of paging messages, scheduling and transmission of Broadcast Channel (BCH) information, dynamic allocation of resources to the UE 10 in both UL and DL, configuration and provision of eNB measurements, radio bearer control, Radio Admission Control (RAC), and connection mobility control in LTE _ ACTIVE state. In the EPC, and as noted above, the gateway 30 may perform the functions of paging initiation, LTE _ IDLE state management, ciphering of the user plane, SAE bearer control, and ciphering and integrity protection of NAS signaling.

Fig. 3 shows a block diagram of a user plane protocol stack of an LTE system. Fig. 4 shows a block diagram of a user plane protocol stack of an LTE system. Layers of a radio interface protocol between the UE and the E-UTRAN may be classified into a first layer (L1), a second layer (L2), and a third layer (L3) based on the lower three layers of an Open System Interconnection (OSI) model, which is well known in the communication system.

The Physical (PHY) layer belongs to L1. The PHY layer provides an information transfer service to a higher layer through a physical channel. The PHY layer is connected to a Medium Access Control (MAC) layer, which is a higher layer of the PHY layer, through a transport channel. The physical channels are mapped to transport channels. Data is transferred between the MAC layer and the PHY layer through a transport channel. Between different PHY layers, i.e., a PHY layer of a transmitting side and a PHY layer of a receiving side, data is transmitted via a physical channel.

The MAC layer, the Radio Link Control (RLC) layer, and the Packet Data Convergence Protocol (PDCP) layer belong to L2. The MAC layer provides a service to the RLC layer, which is a higher layer of the MAC layer, via a logical channel. The MAC layer provides a data transfer service on a logical channel. The RLC layer supports transmission of data with reliability. Meanwhile, the function of the RLC layer is realized by a function block inside the MAC layer. In such a case, the RLC layer may not exist. The PDCP layer provides a header compression function that reduces unnecessary control information so that data transmitted by employing IP packets such as IPv4 or IPv6 can be efficiently transmitted over a radio interface having a relatively small bandwidth.

The Radio Resource Control (RRC) layer belongs to L3. The RLC layer is located at the lowest part of L3 and is defined only in the control plane. The RRC layer controls logical channels, transport channels, and physical channels related to configuration, reconfiguration, and release of Radio Bearers (RBs). The RB denotes a service providing L2 for data transmission between the UE and the E-UTRAN.

Referring to fig. 3, the RLC and MAC layers (terminated in the eNB on the network side) may perform functions such as scheduling, automatic repeat request (ARQ), and hybrid ARQ (harq). The PDCP layer (terminated in an eNB on the network side) may perform user plane functions such as header compression, integrity protection, and ciphering.

Referring to fig. 4, the RLC and MAC layers (terminated in the eNB on the network side) may perform the same functions for the control plane. The RRC layer (terminated in an eNB on the network side) may perform functions such as broadcasting, paging, RRC connection management, RB control, mobility functions, and UE measurement reporting and control. The NAS control protocol (terminated in the MME of the gateway on the network side) may perform functions such as SAE bearer management for signaling between the gateway and the UE, authentication, LTE _ IDLE mobility handling, paging origination in LTE _ IDLE, and security control.

Fig. 5 shows an example of a physical channel structure. The physical channel transfers signaling and data between the PHY layer of the UE and the eNB through radio resources. The physical channel is composed of a plurality of subframes in the time domain and a plurality of subcarriers in the frequency domain. One subframe is 1ms and consists of a plurality of symbols in the time domain. A particular symbol of a subframe, such as the first symbol of the subframe, may be used for a Physical Downlink Control Channel (PDCCH). The PDCCH carries dynamically allocated resources such as Physical Resource Blocks (PRBs) and Modulation and Coding Schemes (MCSs).

DL transport channels include a Broadcast Channel (BCH) used to transmit system information, a Paging Channel (PCH) used to page UEs, a downlink shared channel (DL-SCH) used to transmit user traffic or control signals, a Multicast Channel (MCH) used for multicast or broadcast service transmission. The DL-SCH supports HARQ, dynamic link adaptation by varying both modulation, coding and transmit power, and dynamic and semi-static resource allocation. The DL-SCH may also enable the use of broadcast and beamforming for the entire cell.

The UL transport channel includes a Random Access Channel (RACH) generally used for initial access to a cell, an uplink shared channel (UL-SCH) for transmitting user traffic or control signals, and the like. The UL-SCH supports HARQ and dynamic link adaptation by varying transmit power and potentially modulation and coding. The UL-SCH may also enable the use of beamforming.

The logical channels are classified into a control channel for transmitting control plane information and a traffic channel for transmitting user plane information according to the type of information transmitted. That is, a set of logical channel types is defined for different data transfer services provided through the MAC layer.

The control channel is used only for the transmission of control plane information. Control channels provided through the MAC layer include a Broadcast Control Channel (BCCH), a Paging Control Channel (PCCH), a Common Control Channel (CCCH), a Multicast Control Channel (MCCH), and a Dedicated Control Channel (DCCH). The BCCH is a downlink channel for broadcasting system control information. The PCCH is a downlink channel that transmits paging information and is used when the network does not know the location cell of the UE. CCCH is used by UEs that do not have an RRC connection with the network. The MCCH is a point-to-multipoint downlink channel used to transmit Multimedia Broadcast Multicast Service (MBMS) control information from a network to a UE. The DCCH is a point-to-point bi-directional channel used by UEs having an RRC connection that transmits dedicated control information between the UE and the network.

The traffic channel is used only for the transfer of user plane information. Traffic channels provided by the MAC layer include a Dedicated Traffic Channel (DTCH) and a Multicast Traffic Channel (MTCH). DTCH is a point-to-point channel dedicated to one UE for the transmission of user information and can exist in both the uplink and downlink. The MTCH is a point-to-multipoint downlink channel for transmitting traffic data from the network to the UE.

the uplink connection between the logical channel and the transport channel includes a DCCH that can be mapped to the UL-SCH, a DTCH that can be mapped to the UL-SCH, and a CCCH that can be mapped to the UL-SCH. The downlink connection between the logical channel and the transport channel includes a BCCH that can be mapped to a BCH or DL-SCH, a PCCH that can be mapped to a PCH, a DCCH that can be mapped to a DL-SCH, and a DTCH that can be mapped to a DL-SCH, an MCCH that can be mapped to an MCH, and an MTCH that can be mapped to an MCH.

The RRC state indicates whether the RRC layer of the UE is logically connected to the RRC layer of the E-UTRAN. The RRC state may be divided into two different states such as an RRC IDLE state (RRC _ IDLE) and an RRC CONNECTED state (RRC _ CONNECTED). In RRC _ IDLE, the UE may receive broadcast of system information and paging information while the UE specifies Discontinuous Reception (DRX) through NAS configuration, and the UE has been allocated an Identification (ID) that uniquely identifies the UE in a tracking area and may perform Public Land Mobile Network (PLMN) selection and cell reselection. Also, in RRC _ IDLE, no RRC context is stored in the eNB.

In the RRC _ CONNECTED state, the UE has an E-UTRANRRC connection and context in the E-UTRAN, making it possible to transmit and/or receive data to and/or from the eNB. Further, the UE can report channel quality information and feedback information to the eNB. In the RRC _ CONNECTED state, the E-UTRAN knows the cell to which the UE belongs. Thus, the network can send and/or receive data to/from the UE, the network can control the mobility of the UE (handover and inter-Radio Access Technology (RAT) cell change order to GSM EDGE Radio Access Network (GERAN) with Network Assisted Cell Change (NACC)), and the network can perform cell measurements for neighboring cells.

In RRC _ IDEL state, the UE specifies a paging DRX cycle. Specifically, the UE monitors the paging signal at a specific paging occasion of each UE specific paging DRX cycle. The paging occasions are time intervals during which paging signals are transmitted. The UE has its own paging occasion. Paging messages are sent on all cells belonging to the same tracking area. If the UE moves from one Tracking Area (TA) to another TA, the UE sends a Tracking Area Update (TAU) message to the network to update its location.

low cost Machine Type Communication (MTC) UEs are described. Reference may be made to chapter 5 of 3GPP TR36.888 V12.0.0 (2013-06). The solution studied for the provision of LTE-based low-cost MTC UEs should support the following as minimum requirements.

Support as a minimum value a data rate equivalent to that supported by R'99E-GPRS through EGPRS multislot class 2 devices (2 downlink slots (118.4Kbps), 1 uplink slot (59.2Kbps), and up to 3 active slots). This does not preclude the support of higher data rates as long as the cost target is not compromised.

Compared to what is achieved with R99GSM/EGPRS terminals in today's GSM/EGPRS networks, and conceptually compared to that of LTE, enables the average spectral efficiency for low data rate MTC traffic to be significantly improved. The optimization for low-cost MTC UEs should minimize the impact on the spectral efficiency achievable for other terminals (conventional LTE terminals) in LTE release 8-10 networks.

Assume that it is ensured over the same frequency spectrum band that the service coverage footprint of LTE-based low-cost MTC UEs is no longer worse than that of GSM/EGPRS MTC devices (in GSM/EGPRS networks) or "regular LTE UEs" (in LTE networks).

A 20dB coverage improvement target should be made for low cost MTC UEs compared to the LTE cell coverage footprint defined as a "regular LTE UE" design.

ensure that the overall power consumption is not worse than existing GSM/GPRS based MTC devices.

Ensure good radio frequency co-existence with LTE radio interfaces and networks with legacy (release 8-10).

Target operation of low cost MTC UEs and legacy LTE UEs on the same carrier.

Reuse of existing LTE/SAE network architecture.

Solutions should be specified in terms of changes to the version 10 version of the specification.

The research project should consider optimizations for both frequency division multiplexing (FDD) and time division multiplexing (TDD) modes.

The initial phase of the study will focus on solutions that do not necessarily require changes to the LTE base station hardware.

Low cost MTC devices support limited mobility (i.e. seamless handover is not supported; the ability to operate in networks in different countries) and are low power consuming modules.

Coverage enhancements for low cost MTC UEs are described. Reference may be made to chapter 9 of 3GPP TR36.888 V12.0.0 (2013-06). The performance evaluation of coverage enhancement techniques may be analyzed in terms of coverage, power consumption, cell spectral efficiency, regulatory impact, and cost or complexity analysis. Not all UEs will require coverage enhancement, or the same amount of coverage enhancement. These techniques may be implemented only for the needed UEs.

For coverage analysis, the additional coverage requirement for 20dB enhancement is targeted compared to "class 1 UE". Table 1 shows a Minimum Coupling Loss (MCL) table for class 1 UEs.

< Table 1>

Referring to table 1, it can be expected that as the amount of coverage enhancement becomes larger, all channels listed in table 1 need enhancement. For example, if the amount is equal to 20dB, all uplink and downlink channels need to be enhanced because the gap between the maximum MCL and the minimum MCL is 8.6dB for FDD and 2.7dB for TDD. Given that signal reception Radio Frequency (RF) and bandwidth reduction may be used for MTC UEs, and that these techniques will reduce downlink coverage, additional coverage enhancements need to be considered to compensate for this coverage loss.

Assuming a coverage enhancement of x dB is desired, the restricted channel from table 1 with the minimum MCL will be improved by x dB. It should be noted that the coverage enhancement of x dB is at a data rate of 20kbps relative to a class 1 UE. Other channels will need to reduce the enhancement by a total compensation amount equal to x dB minus the difference between MCL and the minimum MCL. The total compensation amount should also include the application of low cost MTC technology: the signal reception RF chain would require additional coverage compensation for all downlink channels and the reduction of the maximum bandwidth may require additional coverage compensation for (E) PDCCH and Physical Downlink Shared Channel (PDSCH).

The required system functions for MTC UEs in coverage enhancement mode are assumed to include functions required for synchronization, cell search, power control, random access procedures, channel assessment, measurement reporting, and DL/UL data transmission (including DL/UL resource allocation). MTC users moving around may not be out of coverage for a long time. Thus, the goal of coverage enhancement is primarily for non-mobile delay tolerant low cost MTC devices. The system functional requirements of large delay tolerant mtues requiring coverage enhancement may be relaxed or simplified compared to those required for normal LTE UEs. HARQ Acknowledgement (ACK)/non-acknowledgement (NACK) for PUSCH transmission is carried by a Physical HARQ Indicator Channel (PHICH). PHICH may or may not be required depending on the technology of coverage enhancement. A Control Format Indicator (CFI) in a Physical Control Format Indicator Channel (PCFICH) is transmitted in each subframe and indicates the number of OFDM symbols used for transmission of control channel information. The PCFICH may be excluded by some additional complexity of the UE (e.g., decoding of control channels that assume different CFIs) or higher layer signaling (e.g., pre-configuration of CFIs).

Various concepts for coverage enhancement are described.

More energy can be accumulated by extending the transmission time to enhance coverage. Existing Transmission Time Interval (TTI) bundling and HARQ retransmissions in the data channel can be useful. It should be noted that since the current maximum number of UL HARQ retransmissions is 28 and TTI bundles up to 4 consecutive subframes, TTI bundles with larger TTI bundle sizes may be considered and the maximum number of HARQ retransmissions may be extended for better performance. In addition to TTI bundling and HARQ retransmission, repetition can be applied by repeating the same or different Redundancy Version (RV) multiple times. In addition, code spreading in the time domain can also be considered to enhance coverage. The MTC traffic packets can be RLC segmented into smaller packets. Very low rate coding, lower modulation order (binary phase shift keying (BPSK)), and shorter length Cyclic Redundancy Check (CRC) may also be used. New decoding techniques (e.g., correlation or reduced search space decoding) can be used to enhance coverage by taking into account characteristics of a particular channel (e.g., channel periodicity, rate of parameter change, channel structure, limited content, etc.) and relaxing performance requirements (e.g., delay tolerance).

the eNB can use more power in DL transmissions to MTC UEs (i.e., power boosting), or a given power level can be concentrated at the eNB or UE as reduced bandwidth (i.e., Power Spectral Density (PSD) boosting). The application of power boost or PSD boost will depend on the channel or signal under consideration.

The performance requirements for some channels can be relaxed in extreme scenarios taking into account the features of MTC UEs (e.g., greater delay tolerance). For the synchronization signal, the MTC UE can accumulate energy by combining the Primary Synchronization Signal (PSS) or the secondary Synchronization Signal (SS) multiple times, but this will lengthen the acquisition time. A relaxed PRACH detection threshold rate or a higher false alarm rate at the eNB can be considered for the Physical Random Access Channel (PRACH).

If the implementation-based approach fails to meet the coverage enhancement requirements, a new design of channels or signals for better coverage is possible. These channels and signals, as well as other possible link-level solutions for coverage enhancement, are summarized in table 2.

< Table 2>

coverage enhancement using link improvement must be provided for the case where the operator has not deployed a small cell. Operators may deploy traditional coverage enhancement solutions using small cells (including pico (pico), femto (femto), Remote Radio Head (RRH), relays, and the like) to provide coverage enhancement to MTC and non-MTC UEs and the like. In deployments with small cells, the path loss from the device to the nearest cell is reduced. As a result, for MTC UEs, the required link budget can be reduced for all channels.

For deployments that already contain small cells, there may be a benefit of further allowing decoupling UL and DL for delay tolerant MTC UEs. For the UL, the best serving cell is selected based on the minimum coupling loss. For DL, the best serving cell is the cell with the largest received signal power due to the large Tx power imbalance (including antenna gain) between the large and Lower Power Nodes (LPNs). This UL/DL decoupling combination is feasible for MTC traffic, especially services that do not have strict delay requirements. To enable UL/DL decoupling operations in a UE transparent or non-transparent manner, large serving cells and potential LPNs may need to exchange information of channel configuration (e.g., RACH, PUSCH, Sounding Reference Signal (SRS)) and identify a suitable LPN. A different RACH configuration may need to have decoupled UL/DL compared to not.

existing solutions to coverage enhancement deployment for "normal LTE UEs", such as directional antennas and external antennas, can also enhance coverage for MTC UEs and normal UEs.

As described above, repetition of each message can be considered as the basic method of coverage enhancement. Whether the UE needs coverage enhancement may change due to a change of radio channel or movement of the UE. For example, if the UE moves from the basement to the ground, the UE may have a better radio channel and thus the UE may not need to repeat. However, the network cannot know such a change of coverage enhancement, so unnecessary repetition of the UE may occur.

In order to solve the above-mentioned problems, a method for indicating a change of a Coverage Enhancement (CE) mode according to an embodiment of the present invention is described below. According to an embodiment of the present invention, a CE mode is newly defined, and the UE determines whether the CE mode is changed. The UE performs UE-initiated detach if the CE mode changes and performs re-attach through the changed CE mode if the CE mode changes. Thus, the network can know whether a coverage enhancement scheme is needed for the UE in RRC _ IDLE.

Fig. 6 illustrates an example of a method for indicating a change of a CE mode according to an embodiment of the present invention. The CE mode may be defined by whether the UE is required to perform repetition for successful UL transmission and/or DL reception. For example, CE mode 0 may indicate that repetition is not required, and CE mode 1 may indicate that repetition is required. Alternatively, the CE pattern may be defined by the amount of repetition (or number of resource blocks, number of subframes) required for successful UL transmission and/or DL reception. For example, CE mode 0 indicates that no repetition is needed, CE mode 1 indicates that a certain amount of repetition is needed, CE mode 2 indicates that a larger amount of repetition is needed than is needed for CE mode 1, and so on. The UE may transmit information on the CE mode when the UE performs an RRC connection procedure, an attach procedure, or a Tracking Area Update (TAU) procedure. Further, information on the CE mode may be mapped to code points or bits.

Referring to fig. 6, in step S100, the UE determines whether the CE mode is changed. The change in CE mode may indicate that a UE that has performed coverage enhancement does not need to perform coverage enhancement any more. Alternatively, the change in CE mode may indicate that a UE that has not performed coverage enhancement needs to perform coverage enhancement. Alternatively, a change in CE mode may indicate a required/expected amount of repetition (or number of resource blocks, number of subframes) of a coverage enhancement change (e.g., a fewer or greater number of repetitions/resource blocks/subframes are required than is required for the last successful transmission/reception). Further, once the RRC connection is successfully established, the UE may maintain the same CE mode during the established RRC connection.

The UE may determine its CE mode based on various factors. First, the UE may determine its CE mode based on radio channel conditions, such as Reference Signal Received Power (RSRP) and/or Reference Signal Received Quality (RSRQ). In this case, the measured signal level may be compared to a threshold value signaled by the network. For example, coverage enhancement may be needed if RSRP (or RSRQ) < CE _ low, and may not be needed if RSRP (or RSRQ) > CE _ low. When multiple levels of CE mode are defined, coverage enhancement with CE mode 0 may be needed if RSRP (or RSRQ) < CE _ thresh0, and coverage enhancement with CE mode 1 may be needed if CE _ thresh0 ≦ RSRP (or RSRQ) < CE _ thresh1, and so on.

Alternatively, the UE may determine its CE mode based on the necessary system information acquisition period. Coverage enhancement may be required if the UE cannot acquire the necessary system information for the period T _ sys. Alternatively, coverage enhancement may be needed if the UE performs N attempts of necessary system information acquisition, but the UE is unable to acquire.

Alternatively, the UE may determine its CE mode based on the number of repetitions needed to successfully receive system information (e.g., Master Information Block (MIB), system information block type 1(SIB1), sib2.). For example, if the number of repetitions required to receive the necessary system information is 1, coverage enhancement may not be required. Coverage enhancement with CE mode 1 may be needed if 1< required number of repetitions < thresh 1. Coverage enhancement with CE mode 2 may be needed if thresh1< required number of repetitions < thresh2, and so on.

Alternatively, the UE may determine its CE mode based on synchronization channel acquisition, i.e., Primary Synchronization Signal (PSS)/Secondary Synchronization Signal (SSS). Similar to the CE mode determination method by using the above system information, the UE may determine its CE mode based on the number of repetitions required to detect the PSS/SSS. Alternatively, if the UE cannot successfully acquire the synchronization channel for the period T _ sys, coverage enhancement may be required.

Returning to fig. 6, if the CE mode change is determined, the UE is separated from the network in step S110. In step S120, the UE re-attaches with the network based on the changed CE mode. During the re-attach procedure, the UE may include a message regarding the changed CE mode in the attach request message. Thus, the network can know the CE mode of the UE.

Alternatively, during steps S110 and S120, if the AS layer determines a CE mode change, the AS layer may notify the NAS layer of the CE mode that has been changed. Therefore, the NAS layer can always be informed of the latest CE mode of the UE by the AS layer. The NAS layer may store the latest CE pattern and trigger an RRC connection procedure involving a random access procedure. Alternatively, the AS layer itself may initiate the RRC connection procedure. The UE may attempt an RRC connection setup procedure (including a random access procedure) using the changed CE mode. And after establishing the RRC connection, the UE may inform the eNB of the changed CE mode, and the eNB may inform the MME of the changed CE mode.

Alternatively, during steps S110 and S120, if the AS layer determines a CE mode change, the AS layer may notify the NAS layer of the changed CE mode. Thus, the NAS layer can always inform the AS layer of the latest CE mode of the UE. If the stored CE pattern is different from the advertised CE pattern from the AS layer, the NAS layer may store the advertised CE pattern and trigger a TAU procedure. During the TAU procedure, the UE may include the changed CE mode in the TAU request message so that the core network (i.e., MME) knows the latest CE mode of the UE. Also, the NAS layer may inform the AS layer so that the AS layer can perform the RRC connection setup procedure using the latest CE mode.

Fig. 7 illustrates another example for indicating a change of a CE mode according to an embodiment of the present invention. In step S200, the UE turns on the power. In step S210, the UE estimates the CE mode and assumes that coverage enhancement by CE mode 1 is required. Accordingly, in step S220, the UE attaches to the network based on CE mode 1. During the attach procedure, information about CE mode 1 may be sent to the network. In step S230, the UE estimates the CE mode again, and in step S240, the UE determines that the CE mode is changed during being attached. Assume that the CE mode changes from CE mode 1 to CE mode 2. Thus, in step S250, the UE-initiated detach procedure is triggered and the UE performs the detach procedure. In step S260, the UE re-attaches with the network based on the changed CE mode, i.e., CE mode 2. During the reattachment procedure, information about CE mode 2 may be sent to the network. Thus, the network can know the CE mode of the UE.

Fig. 8 is a diagram illustrating a wireless communication system implementing an embodiment of the present invention.

The eNB 800 may include a processor 810, a memory 820, and a Radio Frequency (RF) unit 830. The processor 810 may be configured to implement the proposed functions, procedures and/or methods described in this specification. Layers of a radio interface protocol may be implemented in the processor 810. The memory 820 is operatively coupled with the processor 810 and stores various information for operating the processor 810. The RF unit 830 is operatively coupled with the processor 810 and transmits and/or receives a radio signal.

The UE 900 may include a processor 910, a memory 920, and an RF unit 930. The processor 910 may be configured to implement the proposed functions, processes, and/or methods described in this specification. Layers of a radio interface protocol may be implemented in the processor 910. The memory 920 is operatively coupled to the processor 910 and stores various information for operating the processor 910. The RF unit 930 is operatively coupled with the processor 910 and transmits and/or receives a radio signal.

The processors 810, 910 may include Application Specific Integrated Circuits (ASICs), other chipsets, logic circuitry, and/or data processing devices. The memory 820, 920 may include Read Only Memory (ROM), Random Access Memory (RAM), flash memory, memory cards, storage media, and/or other storage devices. The RF units 830, 930 may include baseband circuits to process radio frequency signals. When an embodiment is implemented in software, the techniques described herein may be implemented with modules (e.g., procedures, functions, and so on) that perform the functions described herein. Modules may be stored in the memories 820, 920 and executed by the processors 810, 910. The memory 820, 920 can be implemented within the processor 810, 910 or external to the processor 810, 910, in which case the memory 820, 920 can be communicatively coupled to the processor 810, 910 via various means as is known in the art.

In view of the exemplary systems described herein, methodologies that may be implemented in accordance with the disclosed subject matter have been described with reference to several flow diagrams. While, for purposes of simplicity of explanation, the methodologies are shown and described as a series of steps or modules, it is to be understood and appreciated that the claimed subject matter is not limited by the order of the steps or modules, as some steps may occur in different orders or concurrently with other steps from that shown and described herein. Additionally, those skilled in the art will appreciate that the steps illustrated in the flowcharts are not exclusive and may include other steps or that one or more steps in the example flowcharts may be deleted without affecting the scope and spirit of the present disclosure.

Claims (13)

1. A method for execution by a User Equipment (UE) in a wireless communication system, the method comprising:

Detaching, by the UE, from a network when a Coverage Enhancement (CE) mode change is determined;

Re-attaching, by the UE, with the network based on the changed CE mode; and

Transmitting information about the changed CE mode to the network during a re-attach procedure,

Wherein the information on the changed CE mode is transmitted via an attach request message.

2. The method of claim 1, wherein the CE mode is defined by whether the UE is required to perform repetition of Uplink (UL) transmission or Downlink (DL) reception for coverage enhancement.

3. the method of claim 1, wherein the CE mode is defined by a number of repetitions required for successful UL transmission or DL reception for coverage enhancement.

4. The method of claim 1, wherein the change in the CE mode indicates that the UE that has performed coverage enhancement no longer needs to perform coverage enhancement.

5. The method of claim 1, wherein the change in the CE mode indicates that the UE that has not performed coverage enhancement needs to perform coverage enhancement.

6. The method of claim 1, wherein the change in the CE mode indicates a required change in a number of repetitions for coverage enhancement.

7. The method of claim 1, wherein the CE mode is determined based on radio channel conditions compared to a threshold signaled by the network.

8. The method of claim 1, wherein the CE mode is determined based on a repetition number or a system information acquisition period for acquiring system information.

9. The method of claim 1, wherein the CE mode is determined based on a number of repetitions for acquiring a synchronization signal or a synchronization signal acquisition period.

10. the method of claim 1, wherein the information on the changed CE mode is mapped to a code point of a bit.

11. A User Equipment (UE) in a wireless communication system, the UE comprising:

A Radio Frequency (RF) unit configured to transmit or receive a radio signal; and

A processor coupled to the RF unit and configured to:

When it is determined that a Coverage Enhancement (CE) mode is changed, separating from the network;

Reattaching to the network based on the changed CE pattern, an

Transmitting information about the changed CE mode to the network during a re-attach procedure,

Wherein the information on the changed CE mode is transmitted via an attach request message.

12. The UE of claim 11, wherein the CE mode is defined by whether the UE is required to perform repetition of Uplink (UL) transmission or Downlink (DL) reception for coverage enhancement.

13. The UE of claim 11, wherein the CE mode is defined by a number of repetitions required for successful UL transmission or DL reception for coverage enhancement.